Electromagnetic heating unit



c. F. scHRoEDER ELECTROMAGNETIC HEATING UNIT Feb. 28, 1967 originalFiled Nov. 5o, 1962 3 Sheets-Sheet l .1 I IIIIIF s (I 1 Fig 3 Feb- 281967 c. F. scHRoEDER 3,307,007

ELECTRC'MAGNETIC HEATING UNIT Original Filed Nov. 50, 1962 3Sheets-Sheet 2 INVENToR. kan 5 .E 5641961505@ Feb. 28, 1967 C, F,SCHRQEDER 3,307,007

-ELECTROMAGNETIC HEATING UNIT Original Filed Nov. 30, 1962 3Sheets-Sheet 5 INVENTOR. 6mm 5 F SCH/mma@ United States Patent O3,307,007 ELECTRMAGNE'IIC HEATING UNIT Charles F. Schroeder, 2317Valleybroolr Drive, Toledo, Ohio 43615 Original application Nov. 30,1962, Ser. No. 241,208, now Patent No. 3,265,851, dated aug. 9, 1966.Divided and this application Oct. 21, 1965, Ser. No. 499,895 6 Claims.(Cl. 219-10.49)

This application is a division of my copending application Serial No.241,208, led on November 30, 1962, now Patent No. 3,265,851.

The present invention relates to an electromagnetic transformer unit,and more particularly, a heater unit utilizing a closed secondarywinding in such manner as to make the unit adaptable to performance in awide range of specific devices for different heating purposes.

According to the present invention, a magnetic circuit construction isprovided which, although capable of design for operation at any of awide range of frequencies, is highly adaptable to the translation ofelectrical energy into heat energy at the usual commercial frequenciesof 50 or 60 cycles and even lower frequencies, such as 25 cycles stilloccasionally encountered in practice.

It is a purpose of the invention to provide a magnetic circuitconstruction incorporating principles which make it ladaptable toprovision of heating units for translation of electrical energy intoheat energy at commercially available power frequencies with a minimumof cost in equipment.

It is another object of the invention to provide a new electricalheating unit flexibly adaptable to any of a wide variety of uses byproportional changes in shape within the latitude of variation permittedby the principles ernployed.

In brief, the operating elements of the construction of the inventionincludes a magnetic core energized by a primary winding, and a singleturn secondary loop which sur-rounds both the core and primary toprovide a heating unit arrangement flexibly utilizable for either homeappliance of industrial purposes. This is accomplished in general bysurrounding a magnetic circuit loop with a secondary, not only closedabout the cross section of the core, but also extending along the lengthof the magnetic circuit and forming a closed loop.

A feature of the invention lies in its adaptability in design topractically any commercial voltage and frequency without need forspecial auxiliary frequency-generating equipment.

Another feature of the invention lies in its ruggedness of constructionand adaptability to provision of selective surface areas to be heated tohigh temperatures, while other portions of the unit remain substantiallycool.

Still another yfeature of the construction of this invention lies in itsefciency in translation of electrical energy into heat energy, and theadaptability lof the principles to practically any size construction.

Although for purposes of illustration, this invention is hereindescribed in connection with the translation of electrical energy intoheat, it will 'be understood upon review of the embodiments disclosed,that they are adaptable for other purposes as well, such for example, aswhere large magnet flux concentration are desirable and are produced asa result of high currents in the closed secondary loop.

Other objects and features which are believed to be cha-racteristic ofmy invention are set forth with particularity in the appended claims. Myinvention, however, both in organization and manner of construction,together with further objects and features thereof, may be bestunderstood by reference to the following description taken in connectionwith the accompanying drawings, in which:

FIGURE 1 is an isometric view, partially broken away and partially incross-section, illustrating a magnetic circuit construction embodyingthe principles of my invention;

FIGURE 2 is an isometric view, partially broken away and partially incross-section, of an electrically heated lcettle emboding the magneticcircuit principles of my invention:

FIGURE 3 is a partially broken away `and partially cross-sectional viewof an extrusion press cylinder embodying a plurality of magnetic circuitsections according to the principles of my invention;

FIGURE 4 is an isometric partially broken cross-sectional view of ahot-plate type unit embodying the principles of the magnetic circuitconstruction of this invention;

FIGURE 5 is an isometric broken cross-sectional view of a frypanconstruction embodying the closed secondary magnetic circuit principlesof the present invention;

FIGURE 6 is a somewhat schematic isometric view partially broken awayand partially in cross-section of a heater strip embodying theprinciples of the present inventio-n;

FIGURE 7 is an enlarged broken cross-sectional view of a portion of theheater strip of FIGURE 6; and

FIGURE 8 is a semi-schematic illustration of a heating unit embodyingthe principles of the present invention adapted to integral associationof -a temperature control circuit.

Referring to the drawings in greater detail, FIGURE 1 shows the generalarrangement of components of a transformer type construction 10employing a single turn secondary loop wherein the single turn loopcomprises the outer shell made up of van annular member of U-shapedcross-section capped by a -at ring-shaped capping member which forms anenclosure and completes a closed electrical loop for an annular magneticcore 13 residing therein. The ring-shaped cap 12 and the annular U-shaped member 11 are both of electrically conducting material such asaluminum, steel, copper, zinc, etc., capable of permitting a lowresistance juncture of the ring cap 12 and the member 11 to establish alow resistance loop about the magnetic core enclosed therein. Themagnetic core 13 is made up of magnetic ilux path segments and in thisrespect, can for example, be a spiral-wound core or a series o-f stackedannular discs or even a magnetic wire Wound core. The primary orenergizing winding 14 is wound directly on the core over electricalinsulation of high temperature-resistant properties. The primary windingas illustrated may extend over the full length of the core, andcorrespondingly extend through the interior of the annular secondary forits entire length.

The leads 15 for the primary winding 14 are connected to plug-typeconnector prongs 17 mounted on an insulating member 16 installed in theside of the annular secondary.

FIGURE l illustrates that the annular members 11 and 12, in a sense,form a pair of secondary loops. One closed loop is formed by thecross-sectional path-of the shell for the core 13, longitudinally by theannular shape of the shell.

In operation, energization of the primary winding 14 generates amagnetic flux in the core 13. This flux cuts the walls of thesurrounding shell and generates a secondary current, having a pathextending around the crosssection of the shell. This is illustrated bythe dashed-line loop drawn in the shell wall in FIGURE 1. Since themagnetic flux alternates, the current flow in the crosssectional loop isalso alternating. Accordingly, double headed arrows are utilized toillustrate the path of flow of such current. Any tendency toward fluxleakage diametrically across the annular core results in generationwhile the other loop is provided of an annular -current iiow, inaddition to the ow in the cross-sectional loop. Sufficient current canbe readily made to ow, particularly in the cross-sectional loop, toresult in the temperature of the unit being raised to a degreepermitting its utilization as a heater unit.

FIGURE 2 shows a heating kettle embodying the principles of thetransformer unit of FIGURE 1 for translation of electrical energy intoheat for cooking purposes. In this embodiment, the closed loop secondaryis formed of the hollow shell-like walls of the kettle made up of athick outer wall 21 and a thin inner wall 22. Since the current ow inthe secondary is predominantly in the cross-sectional loop, the currentow in the thick outer wall equals that of the thin interior wall of thekettle. Thus, when the annular-shaped core 23 encased within thecross-sectional loop is energized by the primary coil 24 wound thereon,the current flow in the cross-sectional loop will cause by far thegreatest 12R loss in the interior wall 22 effecting translation of theenergy into heat. In the opposite sense, however, the outer -thickerwall 21 of the cross-sectional loop can be made suiciently thick that itwill remain relatively cool while the interior wall 22 is raised todesired temperature.

Although the core 23 is shown extending through substantially the fullheight of the heating kettle, it can also be made shorter under certainelectrical design criteria and not so long as to extend through the fulllength of the hollow walled structure. That is, the hollow interior ofthe unit can be made to extend a distance beyond the core and also bemade narrower, if desired, to conform to desired exterior designconfigurations.

Upon reviewing the path of current flow in the secondary briey, again itwill be noted that when the magnetic llux build-up and -collapse occurswithin the core 23, the current flow in the closed secondary loop formedby joinder of the thin interior wall 22 to the thicker exterior throughthe overhanging edge of the thick wall-section 21 and its bridgingbottom portion 26, can be made such that the temperature of the interiorwill be raised appreciably while the thicker sections 21 and 26 periencean appreciable rise in temperature. Thus, the exterior of the heatingkettle can be maintained cool, while the interior is of sufiicienttemperature to heat its contents, such as food placed therein to becooked.

To further enhance the etlieiency of utilization of the kettle, theexterior can be made of relatively low electrical resistance materialssuch as aluminum, while the interior is made of steel having higherresistivity as Well as a magnetic hysteresis which will provide acorresponding larger capability for generation of heat with a givenmagnitude of current flow in the secondary loop. Electrical and thermalinsulation 28, such as asbestos or fibrous glass, is inserted betweenthe core 23 and the interior wall 22 to both electrically isolate thewalls and to thermally insulate the core from the hot interior wall.Thus, the core, by having an interior diameter dimension somewhat largerthan the diameter of the thin interior wall, is both isolated by spaceas well as the thermal insulation interposed therein. The interior walland the exterior walls are joined such as by welding them together attheir zone of juncture at the top of the kettle as at the bridgingprojection 26. If desired, the exterior can be coated with a protectivelayer of material such as an epoxy resin. Handles 29 are provided at theexterior and an electrical plug 25 connected to the winding 24 isprovided for convenient connection to a power source such as a 60 cyclepower source.

FIGURE 3 illustrates another unit incorporating the transformerconstruction of my invention for heating purposes. This apparatusutilizes a series of circular transformer sections physically aligned toform a hollow cylinder such as the interior of a resin extrusion press.The common interior wall 32 of the cylinder is raised to a desiredtemperature while the thicker exterior which makes a series of adjacentclosed loop s econdaries with will not exthe interior wall 32 ismaintained relatively cool. Within each closed loop secondary is amagnetic core of annular shape 33 extending about the cylindricalinterior. Each core 33 is enclosed by the outer shell 31 which providesa pair of radially inwardly extending annular projections 35 located onopposite sides of the core between the shell and the interior wall 32.The interior wall 32 is sufficiently thin in dimension that it can bereadily heated by current ow therethrough while the exterior shell 31 oflarger thickness will not become appreciably heated by the same current.Each core 33 has an insulated primary winding 34- wound thereon whilethermal insulating material is interposed between the core and theinterior wall 32 of the cylinder. Thus, the core is thermally andelectrically insulated from the interior wall.

The series of spaced cores 33 so arranged about and along the length ofthe interior wall 32, are well adapted to independent energization ofadjacent zones to establish different desired temperatures along thelength of the cylinder. At the front of the cylinder, a nozzle 36 isprovided, as shown in dotted lines, having an aperture 39 through whichmaterial from the interior of the cylinder is extruded into a mold 37also outlined in dotted lines. A feature of this arrangement lies inthat the material extruded under pressure from such cylinder can beintimately regulated so that the material can be heated or allowed tocool to different temperatures at each stage of its path of progressionalong the length of the cylinder.

FIGURE 4 illustrates still another embodiment of the present inventionwherein the transformer principles are utilized for generation of heatin a hot-plate type unit. In this construction, the hot-plate unit 4@ isformed of a circular electrically conducting base 41 having an annularrecess therein for receipt of a magnetic core 43, also of annular shape.The core 43 has a primary winding 44 wound thereon over i-ts full lengthand energized through the exterior wall of the recess by way of leads 45connected to suitable exterior power source. The circular base is cappedby a thin plate 42 enclosing the core 43. The recess in the base issufficiently deep that thermal insulation 4S can be interposed betweenthe plate and the core with its energizing winding thereon. The base canbe made of material having a low resistivity such as aluminum, while thethin cap plate is made of a higher resistivity material such as steel sothat current flow in the loop formed by the base member and the coveringplate is most effective in translating the electrical energy into heatwithin the plate 42. The steel plate will generate heat due to bothhysteresis and eddy current losses in addition to resistance losses dueto the secondary current iiow therein. The juncture between the basemember and the cover plate 42 can be effected in zones of smallercross-section formed by bevelling the base portions contacting the plateso that heat transmission to the base from the cover plate is minimized.

FIGURE 5 illustrates a fry pan unit utilizing the principles of thetransformer construction of FIGURE 4 in which the exterior of thetransformer remains cool while only the interior zones are raised to arelatively high temperature. In this connection, the core 53 is a iiatannular shape with an insulated primary winding 54 wound directlythereon extending over the full length of the annual and enclosed Ibythe base 51 of thick crosssection forming a loop with an inserted flatplate member 52 having an upwardly extending wall Sti. The outer shellformed of the base 51 has an upwardly projecting overhanging lip section59, while the plate member -52 inserted therein engages the interior ofthe lip 59 by way of its wall Si) to form an electrical loop therewith.The shell 51 `also has a central projection `5S centrally engaging theunder portion of the plate member 52; thereby forming a closed annularsecondary loop about each increment of length of the core 53. Thewinding 54 on the core 53 has a pair of leads 55 extending through thewall of the shell 51 to a suitable connecting plug (not shown) on thehandle 6 of the fry pan. Thermal insulation '57 is interposed betweenthe core 53 and the lbottom of the hot plate 52 t-o thermally insulatethe core from the heating portion of the fry pan.

FIGURES 6 and 7 illustrate a kitchen-range type electrical heatingelement embodying the principles of this invention. The heating elementhere is shaped generally to look like those used in kitchen electricalranges Ibut utilizes magnetic principles in conjunction with the usualresistance heating principles to translate electrical energy into heat.An annular tube 61 of electrically conducting material encloses a core63 of magnetic material electrically energized by a primary winding 64connected to a pair of connecting prongs 65 adapted for association witha plug 66 connected to a Source of electrical energy. The magnetic coreis embedded within a high temperature resistant electrical insulatingmaterial such as a ceramic material 68 and can be laminated or in theform of a generally circular cable of wire conductors extending aboutthe interior of the annular tube to form a complete annular mangeticcore. The winding 64 generates magnetic flux in the core which cuts thecircular wall of the tube to cause a current ilow therein andconsequently eliect heating of the tube. For more eilicient localtransfer of heat to utensils placed thereon, the tube 61 is providedwith a thin-walled upper portion or top `62 of material having a highelectrical resistivity, thereby concentrating the heat in the upper zoneof the annular loop 61 and correspondingly making it more quicklyresponsive in temperature to energy changes.

The primary winding 64 can be made of resistance wire such as nichromewire, -which of itself will generate heat when energized in a mannersimilar to the electrical resistance heaters conventionally utilized. Inaddition to resistance heating, however, the tube in this arrangementtranslates magnetic energy .into heat directly in the walls of the tube61 before heat is conducted thereto from the resistance wire through theinsulating materials. Thus, a combination of resistance and magneticheating of the tube 61 is provided which is much quicker in startup thanstraight resistance-type heating elements, since heat is generated inthe outer walls as soon as electrical energy is supplied.

To reduce transfer of heat to the magnetic core 63 from the primarywinding, the core is provided with an electrical and thermal insulationcovering 67 such as asbestos paper over which the energizing resist-ancewinding 64 is wound. Both the magnetic core and the resistance wire areelectrically isolated from the outer shell by the ceramic insulatingmaterial 68 within lwhich they' are embedded. Although resistanceheating is here described, the primary can also |be made to generateheat principally by current flow in the surrounding walls as in thearrangement of the foregoing embodiments. W-here the resistance wire isutilized for the primary, however, the core may be more desirablydisposed closer to tbe top of the spa-ce within the tube 61 so that theheat will be more readily conducted, through the heating surface fromthe resistance wire rather than to the side walls or the bottom.

FIGURE 8 illustrates a heating unit and the adaptability of the presentinvention to regulation by temperature control means with-out need forlarge power control elements. In this arrangement, the heating unit isan lassembly -of a closed loop secondary 102 of annular shape enclosinga magnetic core 103, beside being provided with a primary winding 104within the secondary loop 102, has a second or control winding 105 whichprovides a saturating magnetic flux. The primary winding 104 isenergized in conventional manner by the line leads L1, L2 connected to asuitable source of alternating current, while the second winding 105 isconnected to the line leads L1 and L2 through a rectifier 115 and bridgecircuit. The second winding 105 is energized by D.C. under the'controlof a bridge circuit having an associated temperature sensing means suchas a thermistor connected therein. The magnetic ilux generated by theprimary winding 104 thus can Ibe regulated in eifectiveness to translatethe electrical energy into heat by a -setting of manually adjustable-control components associated with the bridge.

The bridge circuit of FIGURE 8 is essentially a Wheatstone bridge typecircuit having a thermistor or other temperature sensing element such asthermocouple 117 connected therein, while the remaining bridgeresistances 118, 119, and 120 are connected so that setting of thevariable resistance 118 will determine the amount of energy convertedinto electrical power in the closed secondary 102, and correspondingly xthe degree of temperature rise and temperature of the tube 102. Thethermocouple is positioned on a section of the secondary which isrepresentative of the temperature of the heating unit, and by settingthe variable resistance 118 to a temperature setting determined bycalibration, the balance of current ow in the bridge determines thesaturating' D.C. current flowing inthe winding 105. The resistance 118can be accurately calibrated for temperature to be maintained at theheating unit so that when a temperature setting is made, -a D.C.magnetic flux will be generated in the core such as will permitgeneration of the proper amount of llux Idue to current flow in thewinding 104 corresponding to the desired temperature.

Saturation of the core 103 by the second winding 105 can Ibe carried toa value such that little or substantially no heating of the secondarytube 102 will occur. On the other hand, the setting can be adjusted sothat the degree of saturation by the D.C. winding is nil to permit fulltranslation of the electrical energy of the winding 104 into heat energyin the tube 102. Thus, with a single setting of the relatively lowcurrent capacity resistance in the bridge circuit, the larger current ofthe secondary tube and translation of electrical energy into heat withinthe system can be xed.

This bridge arrangement however, is only exemplary of one of many bridgecontrol arrangements which can be adapted to the units of the presentinvention. For eX- ample, impedance type bridges, as well as any numberof other type of electrical bridge networks can be utilized with atemperature sensing mechanism to provide saturation controls for settingtemperature of the heating unit.

In View of the foregoing, it will be understood that many variations ofthe present invention can be provided within the broad scope of theprinciples embodied therein. For example, the transformer, although asillustrated, is predominantly adopted to use for heating units, it willbe recognized that the transformer construction as illustrated in FIGUREl can be utilized for other magnetic circuit arrangements, such asprovision of an energizing circuit for still another loop extendedthrough the opening in the annular configuration illustrated. Themagnetic flux concentration in the secondary, and about the secondary ofthe construction is also of novel character, and any number ofadaptations of the transformer principles here disclosed can beaccomplished. Thus, while particular embodiments of the invention havebeen shown and described, it is intended by the appended claims to coverall such modifications which fall within the true spirit and scope ofthe invention.

I claim:

1. An electrically heated hollow container unit comprising a magneticcore forming a magnetic loop surrounding the conlined space of thecontainer, a primary circuit wound on said core, and a secondary circuitfor supply of heat to said container surrounding the crosssection ofsaid core as well as the primary wound thereon to form a closedconductive path thereabout and forming a wall surrounding the coniinedspace region within said container, said closed secondary circuitextending over the full length of said magnetic core and back to itselfto form a second loop thereof enclosing said mag- 7 netic loop as wellas a source of heat for said confined space region.

2. An electrically heated closed bottom container unit comprising amagnetic core forming a magnetic loop, a primary circuit wound on saidcore, and a single turn secondary circuit closed on itself about thecross-section of said core as well as said primary circuit, saidsecondary circuit extending over the full length of said magnetic coreloop and primary circuit and back to itself to form an enclosure forsaid magnetic loop and primary circuit, said single turn secondarycircuit also forming an interior surrounding wall portion of said closedbottom container and providing a source of heat for said container.

3. An electrically heated closed bottom container unit comprising acontainer having a confined interior space yand a double side wall ofelectrically conductive material extending about said coniined interiorspace, a magnetic core extending between walls of said double side wallsforming a magnetic core loop therebetween and also surrounding saidconfined space, a primary circuit wound on said core, the walls of saiddouble side wall of the container being electrically joined above andbelow said core to form a closed electrical secondary loop about thecross-section of said magnetic core loop over the full length of saidcore loop whereby said side wall secondary becomes a source of heat forthe confined interior space of said container subject to energization ofsaid primary.

4. An electrically heated closed bottom container with a coninedinterior space comprising an electrically conductive internal wallsurrounding the space conlined within said container, a magnetic core inthe form of a magnetic loop surrounding said internal wall, a primarycircuit on said core, an electrically conductive outer wall extendingabout the length of said magnetic core loop, said outer wall beingjoined electrically to the back of said inner wall on opposite sides ofsaid core loop to form with said inner wall a closed relatively lowresistance electrical secondary path about the cross-section of saidcore, the lower region of the conned space surrounded by said inner wallbeing bridged by an enclosing wall forming a bottom for said container.

5. An electrically heated container comprising an electricallyconductive internal wall surrounding the space confined within saidcontainer, a magnetic core in the form of a magnetic loop surroundingsaid internal wall, a primary circuit on said core, an electricallyconductive outer wall extending about the length of said magnetic coreloop, said outer wall being joined electrically to the back of saidinner wall on opposite sides of said core loop to form with said innerwall a closed relatively low resistance electrical secondary path aboutthe cross-section of said core, the lower region of the conned spacesurrounded by said inner wall being closed by a bottom for saidcontainer, the resistance of the internal wall portion of saidelectrical secondary path through said internal wall being higher thanthe resistance of the remaining portion of the path about thecross-section of said core whereby said internal wall surrounding saidconfined Vspace is selectively heated to a higher temperature subject toenergization of said primary.

6. An electrically heated container comprising an electricallyconductive internal wall surrounding the space confined within saidcontainer, a magnetic core in the form of a magnetic loop surroundingsaid internal Wall, a primary circuit on said core, an electricallyconductive outer wall extending about the length of said magnetic coreloop, said outer wall being joined electrically to the back of saidinner wall on opposite sides of said core loop to form with said innerwall a closed relatively low resistance electrical secondary path aboutthe cross-section of said core, the lower region of the confined spacesurrounded 'by said inner wall being closed by a bottom for saidcontainer, the bottom region of said inner wall being electricallyjoined to the bottom of said container and the bottom region of saidouter wall being electrically joined to the bottom of said inner wall.

References Cited by the Examiner UNITED STATES PATENTS 607,093 7/1898Snow 219--10.79

RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

1. AN ELECTRICALLY HEATED HOLLOW CONTAINER UNIT COMPRISING A MAGNETICCORE FORMING A MAGNETIC LOOP SURROUNDING THE CONFINED SPACE OF THECONTAINER, A PRIMARY CIRCUIT WOUND ON SAID CORE, AND A SECONDARY CIRCUITFOR SUPPLY OF HAT TO SAID CONTAINER SURROUNDING THE CROSSSECTION OF SAIDCORE AS WELL AS THE PRIMARY WOUND THEREON TO FORM A CLOSED CONDUCTIVEPATH THEREABOUT AND FORMING A WALL SURROUNDING THE CONFINED SPACE REGIONWITHIN